Give the correct answer to the follwing question:
Copper, symbolized as Cu, was named cuprum by the Romans because it was obtained from the island of Cyprus. It occurs in both native and combined states, with copper pyrites being the chief ore. Extraction of copper from its ores involves concentration, roasting, smelting, Bessemerisation, and refining.
i. Which of the following is the chief ore of copper?
ii. The process used to concentrate copper ore is:
iii. During electrolytic refining of copper, the impurities collect at: